Method and device for interlocking stackwise plastic bags, especially bags for automatic machines, by welding

ABSTRACT

The invention relates to a method and a device for interlocking stackwise plastic bags, especially bags for automatic machines, by welding, wherein welding is effected by an interlocking device ( 21 ) integrated into the grip hand ( 17 ) of a robot ( 16 ) with the purpose of simplifying welding.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national stage of PCT/EP99/05398 filed Jul.28, 1999 and is based upon German national application 19839155.2 filedAug. 28, 1998 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a method for interlocking plastic bags instacks, particularly bags for automated machines, through fusion.

BACKGROUND OF THE INVENTION

In the plastic bags of the discussed kind, particularly bags forautomated machines, it is known that during manufacturing the bags areprovided with suspension or stacking openings, in order to enable themto be deposited in packages, immediately after production, on thestacking pins of a stacking chain, thereby forming a stack of bags. Whena sufficient number of bags have been stacked on each pair of stackingpins, the respective pair of stacking pins is moved further, so that onthe next pair of stacking pins of the driven revolving stacking pinchain, stacks of bags can again be formed. In order to insure that ineach stack the individual plastic bags can be kept together, aninterlocking is performed directly on the stacking pin chain. For theinterlocking an interlocking station is required. The latter is not onlyexpensive, but also requires a large amount of space, so that thestacking pin chain is relatively long. Bag stacks of the mentioned kindare known from the German Utility Model 74 29 628. For the interlockingof the bag stacks so-called glow plugs or glow pegs, which after beingintensely heated are pushed through the stack of bags. optionally anopening can be stamped prior to that at the punch-through location. Theinterlocking of the plastic bags in the bag stack takes place directlydownstream of the actual stacking process, i.e. within the area of thepin stacking conveyor. At the end of the pin stacking conveyor theinterlocked bag stack is removed by an operator, optionally againexamined for quality control and finally delivered to a transportstation.

In the case of bag stacks which are not interlocked by fusion but areinterconnected by the insertion of a wire bracket with additional safetyplates or rubber stoppers, due to the numerous steps required for theformation of a bag stack, it has also become known to replace the manualhandling by a robot, as described and represented in detail in EP 0 384281 A1.

OBJECT OF THE INVENTION

It is the object of the invention to provide a low-cost method of thekind mentioned in the introduction, through which the stacking of bagsinto a block (stack or pad) and the securing of the stacked bags byfusion is further simplified.

SUMMARY OF THE INVENTION

In order to achieve this object, in a method of the kind discussed atthe outset, the interlocking of the plastic bags in the stack iseffected through fusion after the bag stack is seized and clamped by agrip hand of the robot, by means of an interlocking device. According tothe invention the bag stack is held on a pair of stacking pins and isseized by clamping by the robot grip hand and subjected to fusionimmediately thereafter. At very high production speeds, the interlockingof the bag stack can even take place during the transport of the bagstack to a transfer station by the robot. This means that no additionaltime is required for the interlocking; moreover the transport time whichis anyway needed by the robot between the pickup of the bag stacks fromthe pin stacking conveyor and the transfer to the delivery station isused for interlocking.

In the new system the interlocking device for the housing and theclamping mechanism are eliminated. Besides the stations freely suspendedstations provided in the pin stacking chain for interlocking purposescan be used for manual or automated correction and supervisionfunctions.

If necessary, the interlocked bag stacks can be suspended via stackingholes in the transfer station, for intermediate storage. In this way theinterlocking locations have enough time to cool down, so that the bagstacks interlocked according to the invention can be packed intocardboard boxes relatively quick.

According to the invention a suitable device for the stackwiseinterlocking of plastic bags, particularly bags for automated machines,through fusion by means of an interlocking device is designed so thatthe interlocking device is integrated in a grip hand of the robot whichpicks up the bag stack from a stack-forming device and transfers it to adelivery station. In this way the grip hand of the robot takes over notonly transport tasks, but at the same time performs the stack formation,whereby an essentially disturbance-free handling of the bag stack fromits pickup from the pin stacking conveyor up to the transfer to thedelivery station results.

In a suitable embodiment of the invention, the interlocking device isfastened to a mounting plate of the grip hand, namely ideally on across-section preferably having T-shaped grooves, which is adjustablysupported on the mounting plate. In this way an adjustment to therespective format of the plastic bags is possible. For the fusionitself, it is sufficient to provide a heat source, for instance two glowplugs arranged at a distance from each other and a cylinder-piston unit,for instance in the form of a pneumatic cylinder, for their adjustment.

It has proven to be particularly suitable when the glow plugs arearranged respectively in the area of a first clamping bar of the griphand, which is adjustable with respect to the second clamping bar of thegrip hand, as well as to the glow plugs.

Optimal conditions for the clamping and the interlocking result whenboth glow plugs are arranged outside the clamping locations of theclamping bars of the grip hand.

In this way it is relatively simple to design the upper clamping bar asa wiper for the interlocked bag stack, when for instance the clampingbar is provided with a passage opening for the respectively arrangedglow plugs.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the invention is shown in the drawing and issubsequently described in greater detail. In the drawing:

FIG. 1 is a side view of a machine for the production of plastic bagswith a pin stacking conveyor and a robot downstream thereof with a griphand having an integrated interlocking device;

FIG. 2 is a top view of the machine shown in FIG. 1;

FIG. 3 is a perspective representation of a separate plastic bag;

FIG. 4 is a corresponding representation of an interlocked bag stackconsisting of several plastic bags;

FIG. 5 is a frontal view of grip hand of the robot with integratedinterlocking device;

FIG. 6 is the pertaining side view; and

FIG. 7 is a top view on the grip hand.

SPECIFIC DESCRIPTION

In FIG. 1 a bag-producing machine 1 is schematically represented, whichis designed and equipped for the production of plastic bags 2 (FIG. 3),particularly of so-called automatic plastic bags. Each plastic bag 2 hasin the area of a filling opening 7 a flap 8 projecting at one side, inwhich two suspension holes 9 are stamped and which are associated withtear-off perforation slots 12 at a small distance from the outer edge11.

The aforedescribed plastic bags are produced from a thermoplastic foilweb, which is unwound from a roll by an unwinding stand not shown in thedrawing and which can be shaped as a tubular foil web. Inside thebag-producing machine 1 the tubular foil web is guided over drivingrollers and a tensioning roller not shown in the drawing. By means of ahole-punching mechanism and a crosscut-welding device not shown in thedrawing, the above-described plastic bags 2 can be produced in the knownmanner. Downstream of the crosscut-welding device a transfer device 3 isprovided, which is finally followed by a pin stacking conveyor 4 with astepwise revolving driven pin stacking chain 5. On the pin stackingchain 5, upright standing stacking pins 10 are fastened in pairs spacedfrom one another. On each of the pairs of pins a bag stack as markedwith 6 in FIG. 1 and FIG. 4 can be formed downstream of the transferdevice 3 in the known manner. On the pin stacking conveyor chain 5 theplastic bags are held merely via the stacking pins 10. For furtherhandling, particularly for the transport of the bag stack 6, the bagstacks 6 have to be interlocked, for instance in the manner shown inFIG. 4. In the corner areas 14 separated in the marginal area 8 byperforation lines 13, interlocking points 15 are produced in a mannerwhich will be described in detail, through which all the plastic bags 2in the stack are interlocked. Bag stacks interlocked this way can bepicked up with the aid of a robot 16 arranged at the end of the pinstacking conveyor, by means of a grip hand 17 and, according to apredetermined control, transferred to a magazine station 18 of adischarge station 20.

The robot 16 with its grip hand, has a multiple function. So forinstance by means of the robot arm (FIG. 1), the bag stack 6 can notonly be picked up from the pin stacking conveyor 4 and transferred tothe discharge station, but at the same time the grip hand 17 can beprovided with an interlocking station 21, which results in detail fromFIGS. 5 to 7. The grip hand 17 is supported by a cylinder-piston unit22, which is swingably supported on an outrigger of the robot 16 at 23.The cylinder-piston unit 22 rests on angle piece 24, on which asubstantially trapezoidal mounting plate 25 is fastened. The mountingplate 25, advantageously made of corrugated aluminum sheet, has on itsfrontal side two spaced-apart guide bars 26, wherein a crossbeam 28 isaxially slidable via a guide element 27. The crossbeam 28 has severalgrooves which in cross section are T-shaped. In the individual groovesare guided the guide element 27 and a ram 29 of the cylinder-piston unit22, while on the frontal side an L-shaped clamping bar 31 and on theunderside angled catch pins 32, whose distance corresponds to thedistance between the suspension holes 9 in the plastic bags 2. Incooperation with the upper clamping bar 31, a lower clamping bar 33 isfastened to the lower end of the mounting plate 25. Both clamping barscan be covered with a plastic lining. In the represented embodimentexample, the upper clamping bar 31 is formed by two clamping barsections arranged at a distance from each other.

The above-mentioned interlocking device 21 has a heat source in the formof two spaced-apart glow plugs 36, of which in FIG. 5 only the glow plugon the left side is shown. The glow plug arranged on the right side withits actuation device is identically designed and therefore notrepresented in detail. Glow plugs, respectively glow pegs of theillustrated kind are known per se. In any case, a cylinder-piston unit37, in the form of a pneumatic cylinder, is required for the axialdisplacement of the glow plug 36. The cylinder-piston unit is adjustablyfastened on the cross-section 28 by means of a holder 38. The upperclamping bar 31 has a passage opening 39 for the glow plug 36. Thedistance between the two glow plugs 36 lies outside the range of thecatch pins 32.

The device according to the invention works as follows:

After a bag stack 6 is formed in the pin stacking conveyor 4, each bagstack 6 reaches the position shown in FIG. 1. There the bag stack, whichis not yet interlocked, is clampingly held between the clamping bars 31and 33 of the grip hand 17 of the robot 16, whereby the catch pins 32engage in the suspension holes 9 of the plastic bags. Immediately afterthe bag stack is seized and gripped, the interlocking of the bag stacktakes place through fusion with the aid of the interlocking device 21integrated in the grip hand 17 of the robot 16. For the purpose ofinterlocking during the clamping of the bag stack, the glow plugs 36serving as a heat source are pushed into the bag stack by means of thepneumatic cylinders 37, namely in the corner areas 14, in order to formthe interlocking locations 15 according to the bag package shown in FIG.4. This interlocking takes place either still in the pin stackingdevice, or more suitably, after the seizing and clamping of the bagstack, the transport of the bag stack to a delivery or discharge stationis carried out. Preferably the interlocking is also performed duringthis transport motion. After a short dwelling time in the bag stack, theglow plug is retracted and the glow plug is brought to its rest positionso that the interlocking locations can be cooled. During retraction, theupper clamping bar 31 functions as a wiper. After interlocking, the bagpackage can immediately be brought to the discharge station 20 by meansof the grip hand of the robot 16, as shown in FIG. 2.

Alternatively it is also possible to bring the interlocked bag stack 6to an intermediate storage, so that the interlocking locations can cooldown. This can be for instance done by bringing the bag stack to acontrol unit 41 (FIG. 2). From this control unit the bag stacks can bemanually boxed, or again be boxed by means of the robot. Finally forcooling the bags can suspended on a plate carousel. Such a platecarousel is indicated in FIG. 2 and comprises guide rollers 42 withmounting plates 43 and brackets 44 fastened thereto.

It has been found that due to the arrangement of the robot at the end ofthe pin stacking conveyor and to its multiple uses for the transport ofthe bag stacks, as well as for the their interlocking, a universal usepossibility is given for a great variety of bags, such asshirt-containing bags, which are interlocked according to the invention.

I claim:
 1. An apparatus for producing stacks of interlocked plasticbags, comprising: a bag-making machine for producing a succession ofplastic bags and including a conveyor having locations each receiving amultiplicity of said bags; a robot arm having a gripper hand engageablewith each multiplicity of bags for lifting same from the respectivelocation and transporting the respective multiplicity of bags away fromsaid conveyor, said gripper hand having: a support engageable beneaththe respective multiplicity of bags and along an edge thereof, aclamping member displaceable toward said support for clamping therespective multiplicity of bags between the clamping member and thesupport, and means on said hand for interlocking the respectivemultiplicity of bags while the respective multiplicity of bags isclamped between said clamping member and said support; and a dischargestation spaced from said conveyor for receiving each stack ofinterlocked bags from said gripper hand.
 2. An apparatus for producingstacks of interlocked plastic bags, comprising: a bag-making machine forproducing a succession of plastic bags and including a conveyor havingspaced apart pairs of pins each receiving a multiplicity of said bagswith the pins of the respective pair engaging through the bags along anedge there of; a robot arm having a gripper hand engageable with eachmultiplicity of bags for lifting same from the respective pair of pinsand transporting the respective multiplicity of bags away from saidconveyor, said gripper hand having: a support engageable beneath therespective multiplicity of bags and along said edges thereof, a clampingmember displaceable toward said support for clamping the respectivemultiplicity of bags between the clamping member and the support, and apair of heated members on said hand adapted to press against therespective multiplicity of bags for interlocking the respectivemultiplicity of bags while the respective multiplicity of bags isclamped between said clamping member and said support; and a dischargestation spaced from said conveyor for receiving each stack ofinterlocked bags from said gripper hand.
 3. The apparatus defined inclaim 2 wherein said gripper hand comprises a mounting plate, a holderhaving grooves which are T-shaped in cross section and adjustablysupported on said mounting plate and a pair of piston and cylinder unitsadjustably mounted on said holder and respectively carrying said heatedmembers for pressing said heated members against the respectivemultiplicity of bags while said respective multiplicity of bags isclamped between said clamping member and said support.
 4. The apparatusdefined in claim 3 wherein said clamping member of said gripper handcomprises a first clamping bar guided on said mounting plate andprovided with a piston and cylinder unit for pressing said firstclamping bar against the respective multiplicity of bags along saidedges thereof and a second clamping bar fixed to said plate and formingsaid support.
 5. The apparatus defined in claim 4 wherein said heatedmembers are glow plugs.
 6. The apparatus defined in claim 5 wherein saidfirst clamping bar has holes through which said glow plugs pass.
 7. Theapparatus defined in claim 6 wherein said first clamping bar is providedwith a pair of spaced-apart catch pins engageable through said bags upondisplacement of said first clamping bar toward said second clamping bar.8. The apparatus defined in claim 7 wherein said glow plugs are locatedoutwardly of said catch pins of said first clamping bar.
 9. Theapparatus defined in claim 2 wherein said clamping member is a firstclamping bar and said support is a second clamping bar, said clampingbars engaging the respective multiplicity of bags between them, saidfirst clamping bar having a pair of catch pins engageable in said bags,said heated members being glow plugs adapted to be pressed into therespective multiplicity of bags.
 10. The apparatus defined in claim 9wherein said glow plugs pass through holes formed in said first clampingbar.
 11. The apparatus defined in claim 10 wherein said glow plugs arelocated outwardly of said catch pins along said first clamping bar.